Device for treatment of bulk material, a method as well as a beam construction intended for said treatment

ABSTRACT

The present invention relates to a device for the treatment of bulk material, comprising a platform  24′, 24′, 28  for supporting bulk material and at least one outfeeding device  28  arranged on the platform for feeding bulk material placed on the platform towards an outlet  29  arranged on the platform, wherein the feeding device has a feeding direction towards the outlet, a first and a second beam  30, 31, 32, 33  is arranged on the platform above the outfeeding device, which beams extends transversal to the feeding direction of the outfeeding device and at least a portion in over of the width of the outfeeding device, wherein the second beam  32  being arranged at a higher level above the outfeeding device than the first beam  31 . Further, the invention comprises a method for the treatment of bulk material, wherein the bulk material is placed on a platform  24′, 24′, 28  comprising an outfeeding device  28  and an outlet  29  arranged in connection to one end of the outfeeding device, and wherein bulk material which is placed on the platform and being fed by the outfeeding device in a direction towards the outlet and is slowed down at several places above the outfeeding device. Additionally, the device comprises a beam construction intended to be used in a device for the treatment of bulk material.

TECHNICAL FIELD

The present invention relates to a device for the treatment of bulkmaterial, comprising a platform for support of bulk material and atleast a belt conveyor arranged on the platform for feeding bulk materialplaced on the platform towards an outlet arranged on the platform, thebelt conveyor having a feeding direction towards the outlet. Further,the invention relates to a method for the treatment of bulk material aswell as a beam construction intended for said treatment.

PRIOR ART

Since long time it is known that bulk material with varying fractionsizes, i.e. a variation in size and/or density, results in coarserand/or heavier fractions rolling or falling down the side of thehillocks of bulk material which are gradually formed in connection withloading, transport, dumping and emptying on e.g. a lorry or a train.

A trough is previously known for discharge of asphalt, comprising abottom and two side walls, a rear wall and a considerably lower frontwall as well as a discharge conveyor arranged at the bottom of thetrough in the form of an endless belt conveyor with a carrier. The beltconveyor is placed centrally in the trough and feeds the asphalt fromthe front wall to a discharge opening at the rear wall of the trough andfurther to a paving device behind the paving machine, where the asphaltis transversally distributed by means of feed screws across the surfaceto be paved.

At asphalting, one aims at a substantially continuous discharge ofasphalt from the trough in order to avoid that joints are formed in thepaved surface at stop of the asphalting. Therefore, the trough isdesigned in such a way that a lorry filled with bulk material may beplaced at the front wall and successively dump its load of bulk materialover the bottom portion. The accumulations of fractionated bulk materialat and along the front and rear walls of the lorry platform arepreferably transferred to the discharge trough at start and stop ofdumping of the load. This gives an additionally increased concentrationof fractionated asphalt at the shifting of lorries, and areas offractionated asphalt are formed in the joint between the loads of twolorries. De resulting areas with coarse and/or heavier fractions get agreatly impaired quality and life time, which results in early andexpensive repairs.

The fractionated areas along the longitudinal walls of the lorryplatform will in a corresponding manner land on the discharge trough. Atthe discharge from the trough said coarse fractions will to a certainextent be carried on by the belt conveyor and form longitudinal strandsin the roadway, but some of said coarse fractions will be not bedischarged but form a residue on both sides of the belt conveyor.

In order to be able to discharge said residue a discharge trough hasbeen developed with tiltable sides, which at the end of each load forcesthe asphalt to fall/slide down towards the belt conveyor. However, ithas proved that the asphalt being tipped from said areas of thedischarge trough, which the belt conveyer does not reach, issubstantially fractionated and/or has an undesirable temperature, whichresults in areas with greatly impaired quality and life time are formedin the paved surface. This way to empty the discharge trough hastherefore been abandoned and the residue appearing on both sides of thebelt conveyor may remain and not be shoveled away until the asphaltinghas been ended for the day.

A method and a device for homogenization of bulk material are knownthrough WO9700124, wherein the bulk material is fed from above into acontainer which is defined towards the sides and discharged by means ofan outfeeding device arranged in the lower region of the container.WO9700124 is characterised in that the bulk material is fed from abovein one end of the container, wherein the bulk material is forced to falldown towards the other end of the container, so that a bed of bulkmaterial with a sloping profile is formed in the container, and wherein,because of the fall, heavier and/or coarser fractions of the bulkmaterial fall more than lighter fractions and in that, during each timeunit, an amount of bulk material is taken from each section of thelength of the container in the feeding direction, which amountcorresponds to the supply of bulk material during the same time unit tothe straight above lying section of the upper surface of the bedcorresponding to said section of the length of the container, wherebythe bulk material is forced to move essentially vertically downwards inthe bed along the entire length of the bed towards said outfeedingdevice, which discharges the material from each section in essentiallythe same rate as new material is supplied to the above lying surfacesegment of the upper surface of the bed.

DISCLOSURE OF THE INVENTION

An object of the present invention is to eliminate or at least minimisethe above mentioned problems, which is achieved by the fact that atleast one beam is arranged on the platform above the belt conveyer,which beam extends transversal to the feeding direction the beltconveyer and over at least a portion of the width of the belt conveyor.

Thanks to the invention, the advantage is achieved that the bulkmaterial being discharged from the device gets an essentially betterhomogeneity. At asphalting a considerably improved paving is obtained,wherein the problems with premature wear because of heavily fractionedasphalt are reduced.

According to an additional aspect of the invention the homogeneity ofthe bulk material may be improved further by the device comprising atleast one first and one second beam, which both are arranged above thebelt conveyer and extend transversal to the feeding direction of thebelt conveyor over at least a portion of the width of the belt conveyor,and wherein the second beam, in the feeding direction, is arrangedcloser to the outlet arranged on the platform than the first beam, andwherein the second beam is arranged at a higher level above the beltconveyor than the first beam. By providing the device with more than twobeams, which are arranged at an ascending level above the belt conveyorin the feeding direction of the belt conveyor an increased homogeneityof the bulk material is achieved.

Because said beam/beams extends/extend across the entire width of thebelt conveyor, a simple and rigid construction is achieved at the sametime as the homogeneity of the discharged bulk material is improvedfurther.

According to another aspect of the invention comparativelycoarse-fractioned bulk material from an area outside the belt conveyormay be fed towards the belt conveyor and up onto it if the platformcomprises at least one co-lateral conveyor arranged in a feedingdirection of the co-lateral conveyor which at least partly is directedtransverse to the feeding direction of the belt conveyor.

If said at least one co-lateral conveyor comprises a feed screw, thefeeding of the bulk material from the side may be controlledcomparatively simply.

As the feed screw, in the direction of the belt conveyor, has an openvolume between the threads of the feed screw, a discharge of bulkmaterial may be allowed along the entire feed screw and an increasedhomogenisation is obtained. As the device comprises a plurality of feedscrews arranged on each side of the belt conveyor in the feedingdirection of the belt conveyor, bulk material may be fed right up to thebelt conveyor from essentially the whole bed of bulk material in thedevice, which also makes it possible to control the discharge fromdifferent regions of the bed.

Because the feed screws extend in over the belt conveyor and that feedscrews arranged closer to the outlet extend further in over the beltconveyor than the feed screws arranged further away from the outlet, itis possible to achieve an improved homogenisation of the bulk material.

As said at least one beam has a non-circular cross section and isrotatable about its longitudinal axis, the height of the beam above theconveyor belt may be adjusted in a very simple manner.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be described more in detail below with reference tothe enclosed drawings, of which:

FIG. 1 schematically shows a conventional trough with an outfeedingdevice in a perspective from the front;

FIG. 2 a schematically shows in a side view bulk material loaded on alorry;

FIG. 2 b schematically shows in a view from behind bulk material loadedon a lorry;

FIG. 2 c schematically shows bulk material and its fractionating in ahillock in cross section;

FIG. 2 d schematically shows a hillock of bulk material and itsfractionating in a view from above;

FIG. 3 schematically shows a conventional trough with an outfeedingdevice with bulk material in a perspective from the front;

FIG. 4 schematically shows, in a perspective from the front, aconventional trough with an outfeeding device with residues of bulkmaterial;

FIG. 5 schematically shows, in a perspective view from the front, afirst embodiment of the invention;

FIG. 6 shows an outline diagram of a first embodiment of the inventionin cross section;

FIG. 7 schematically shows, in a perspective view from the front, apreferred embodiment of the invention;

FIG. 8 schematically shows, in a sectional view, a preferred embodimentof the invention;

FIGS. 9 a-9 c schematically show experiments with transport of bulkmaterial out of a conventional trough;

FIGS. 10 a-10 c schematically show experiments with transport of bulkmaterial out of a trough according to the invention; and

FIG. 11 shows results from experiments in full scale.

DETAILED DESCRIPTION OF DRAWINGS

In FIG. 1 a conventional trough 20 with an outfeeding device is shown,comprising a vertical rear wall 21, two vertical side walls 22′, 22″, avertical two-part front wall 23′, 23″, two bottom portions 24′, 24″, atwo-part belt conveyor 28, and two cylinders 27′, 27″ arranged in thefront of the trough itself. The belt conveyor 28 comprises an endlessconveyor belt 25 with a number of uniformly distributed carriers 26. Thebelt conveyor 28 runs out in the rear edge of the trough through anoutlet 29 placed in the lower edge of the rear wall 21. The outlet 29 isdefined laterally by the bottom portions 24′, 24″, downwards by theconveyor belt 25, and in the upper edge by the rear wall 21. The size ofthe outlet 29 controls the volume of the bulk material being transportedfrom the trough.

In FIGS. 2 a and 2 b, examples are shown of a lorry platform loaded withbulk material 40 with a characteristic fractionating. Accumulations 41′,i.e. regions/volumes with coarser and/or heavier fractions, are formedespecially along the front and back walls of the lorry platform andalong the side walls. On lorries with long platforms accommodatingseveral hillocks after each other, also fractionated regions appearbetween the hillocks.

In FIGS. 2 c and 2 d, a cross section and a view from aboveschematically show how the bulk material 40 is distributed in a hillock.Accumulations 41′ of coarser and/or heavier fractions are especiallyformed in the outer and lower regions of the hillock.

In FIG. 3 a conventional trough 20 is shown with an outfeeding deviceaccording to FIG. 1 and how a hillock of bulk material has been formedby for instance a lorry filled with bulk material having dumped andemptied the bulk material across the bottom portions 24′, 24″ and acrosssaid belt conveyor 28. In FIG. 3 it is also indicated that the coarsestand/or heaviest fractions of bulk material 40, which on the lorryplatform have especially been accumulated along the front wall of theplatform and along the longitudinal sides of the platform, see FIGS. 2a, 2 b, are transferred to the trough and land in approximately the samemanner in the front end of the trough and along its longitudinal sides.Finer fractions from the central regions of the lorry platform fall inthe same way substantially centrally in the trough, essentially on topof the belt conveyor 28.

A paving operation of a certain surface or distance with the length l,the width b by means of a conventional trough 20, where the bulkmaterial consists of e.g. asphalt, will now be described with referenceto what is shown in FIGS. 3 and 4. Typically, a substantially continuouspaving operation is aimed at. The supply of new asphalt to the troughcontinues during the whole length which is intended for the pavingoperation and is performed in such a way that a first lorry A filledwith asphalt drives in front of the trough and places its rear wheelsjust in front of/against the cylinders in the front end 27′, 27″ of thetrough, so that the lorry A will be able to follow the same speed anddirection as the paving machine drives. The lorry A successively tipsits load into the trough 20 of the paving machine. When the first lorryA has emptied its load of asphalt, it will leave its position and placeat the cylinders 27′, 27″ and is replaced by a second lorry B with a newload of asphalt, whereupon the filling process is repeated. The fillingprocess is repeated until the last portion of the distance with thelength l and the width b has been paved and the last lorry has dumpedits load of asphalt.

At the dumping from the first lorry A bulk material is accumulated onboth sides of the belt conveyor 28 on the bottom portions 24′, 24″ andalong the side walls 22′, 22″, which bulk material during and after thedumping in progress from the first lorry A will not be transported awayduring the paving operation, which is shown in FIG. 4. This bulkmaterial essentially consists of coarse fractions which by its ownweight cannot fall down against the belt conveyor 28 but form anaccumulation of an inclined slope of repose down towards the beltconveyor 28. The accumulations form counter-supports for new bulkmaterial being filled in the trough, which implies that the fall outtowards the side walls 22′, 22″ at the following dumpings will bereduced considerably. The residues 40′, 40″ of bulk material from thefirst lorry A, which remain after the completed paving operation, have anon-desired fractionating and/or temperature and will be rejectedalternatively returned to the asphalt works.

At the discharge of the bulk material 40 the belt conveyor 28 moves witha direction from the front wall 23′, 23″ towards the outlet 29 in therear wall 21. Each empty section on the conveyor belt 25, i.e. the spacebetween two carriers 26, which are inserted at the front wall 23′, 23″,is filled with bulk material 40, preferably from the front region of thehillock. This results in an essentially larger volume of bulk materialbeing discharged from the front region of said hillock 40, i.e. theregion of the hillock 40 adjacent to the front wall 23′, 23″. The emptyspace which results in the front region of the hillock of bulk material40 is refilled by new bulk material rolling and falling to that place,which creates a characteristic emptying process from the trough with theinitially mentioned problems in the paved surface as a consequence.

In FIG. 5 a first embodiment of the invention is schematically shown ina perspective view. According to this embodiment a conventional trough20, comprising an outfeeding device in the form of a belt conveyor 28with a conveyor belt 25 with carriers 26, is provided with a beamconstruction 30 which is characteristic for the invention. The beamconstruction 30 comprises at least one first transverse beam 31 placedabove the belt conveyor 28 so that part of the bulk material, which ismoved in the direction towards the outlet by the belt conveyor, isslowed down at at least one place situated above the belt conveyor. Thefirst transverse beam 31 is placed on a height h₁ above the beltconveyor 28 and preferably it is placed in the front half of the trough.The cross-section of the beam may be varied but its shape shall have anessential vertical extension so that it constitutes a transporthindrance for the bulk material. This results in that only a desiredvolume of bulk material from the front portion of the trough 20 isallowed to follow the belt conveyor 28 and pass below the firsttransverse beam 31. In other words, the output of bulk material from thefront portion of the trough may be adjusted by means of said beam.

Preferably, the first transverse beam 31 is placed at a height h₁ abovethe belt conveyor 28 which is lower than the height of the outlet 29,whereby a certain additional amount of bulk material may be fed on tothe belt conveyor from the bulk material in the hillock in a positionbehind the first beam 31. The height h₁ above the belt conveyor on whichthe first beam 31 is placed may be varied depending on how large anoutput of bulk material is wanted in this position. Further, one mustconsider the fraction sizes of the bulk material at the choice oflocation so that the space below the beam gets a height h₁ above thebelt conveyor 28, which allows the coarsest fractions of bulk materialto pass. According to the embodiment shown, the first transverse beam 31has a right attachment angle α towards the bottom portion 24′ and 24″,respectively, i.e. α=90°. Further, the first transverse beam 31 ispreferably placed in the front portion of the trough 20 at a distancefrom the front wall 23′, 23″ and at such a height that dumping of thebulk material from the lorry is not hindered, i.e. so that the platformmay be entirely tilted without striking into the beam. Further, itshould be understood that the distance from the front wall 23′. 23″ tothe first transverse beam 31 is chosen so that bulk material beingdumped from the lorry platform may fall down in front of it, at leastduring the most part of the dumping from the lorry. The beam may befixedly or movably mounted in the trough in a suitable manner. Thesimplest way is to attach each end of the beam by means of bolt jointsor to weld them to the side walls 22′, 22″ or along the edges of thebottom portions 24′, 24″ surrounding the belt conveyor 25. It is alsoconceivable to arrange the beam so that it will be detachable bymounting at least one holder at a suitable place in the trough in whichthe beam is inserted. The beam may also be arranged in a rotatableand/or vertically adjustable holder.

According to a first embodiment of the invention, several transversebeams are preferably used in the beam construction 30, in this examplethree beams 31, 32, 33 placed in succession above the belt conveyor 28.According to this first embodiment, the beams are placed so that thetrough is divided into four, essentially equally long transversesections as seen in the transport direction of the belt conveyor.Further, the beams are placed at a gradually ascending height above thebelt conveyor 2. With such an embodiment, the hillock of bulk materialwill be divided into a number of substantially vertical sections, thelength of which, in the transport direction, principally corresponds tothe distance between two transverse beams. The width substantiallycorresponds to the length of the portion of a transverse beam whichextends in over the conveyor belt. If the transverse beam runs acrossthe entire width of the conveyor belt, as is shown here, the transversalextension will at least correspond to the width of the conveyor belt.Thanks to the invention, a possibility is offered to adjust the outputof bulk material from these different sections of the hillock. Newmaterial is taken from the bottom of the respective section in theregion behind and/or between respective beam 31, 32, 33, and the outputis adjusted by adjusting the height difference, i.e. the height abovethe conveyor belt, between two successive beams, which determines howmuch bulk material is allowed to pass below the next beam.

FIG. 6 is a sketch for showing the principle of function of the firstembodiment of the invention. It should be understood that the sketchdoes not entirely correspond to real conditions. In the figure a trough20 is shown which is provided with a belt conveyor 28 comprising aconveyor belt 25 with carriers 26, a beam construction 30, which ischaracteristic for the invention, with in this case three transversebeams 31, 32, 33.

The first transverse beam 31 is placed in the front portion of thetrough 20 at the distance s₁ from the front wall 23″ and at a firstheight h₁ above the conveyor belt 25. The first height h₁ has beenchosen so that the coarsest fractions of the bulk material are allowedto pass below it and preferably it has been chosen so that a desiredvolume v₁ of bulk material from the front portion of the trough 20 ispermitted to pass.

The second transverse beam 32 is placed in the central portion of thetrough 20 at a distance s₂ from the front wall 23″ and at a second,somewhat higher height h₂ above the conveyor belt 25, which permits anaddition of bulk material to the conveyor belt 25 corresponding to adesired second volume v₂. The second volume v₂ falls essentially on topof the first volume v₁.

The third transverse beam 33 is placed in the rear portion of the trough20 at a distance s₃ from the front wall 23″ and at a third, stillsomewhat higher height h₃ above the conveyor belt 25, which permits afurther addition of bulk material to the conveyor belt 25 correspondingto a desired third volume v₃. The third volume v₃ falls essentially ontop of the second volume v₂.

Through the outlet 29, which is placed in the lower edge of the backwall 21, bulk material is discharged by the belt conveyor with thevolume V, which comprises the sub-volumes v₁, v₂, v₃. Further the heightof the outlet 20 is chosen such that a desired volume v₄ is taken fromthe bulk material being close to or in direct connection to the backwall 21 of the trough 20. The fourth volume v₄ falls essentially on topof the third volume v₃. Thus, the totally discharged volume V of bulkmaterial consists of bulk material having been supplied by the conveyorbelt at several positions during the discharge movement of the conveyorbelt, i.e. from the respective section as described above. Consequently,the discharged volume V of bulk material may be afforded an essentiallyimproved homogeneity as compared to the use of a conventional dischargetrough, where the bulk material has substantially been taken from thefront portion of the hillock, as described above with reference to FIG.3.

Thus, according to the invention, if the beam construction 30 comprisesmore than one transverse beam the following conditions are valid betweenthe beams:h _(n) <h _(n+1) <h _(n+2),where h_(n) is the height of the first beam above the conveyor belt,h_(n+1) is the height of the second beam above the conveyor belt, etc.,ands _(n) <s _(n+1) <s _(n+2),where s_(n) is the distance from the front wall 23″ to the first beam,s_(n+1) is the distance from the front wall 23″ to the second beam, etc.

In order to avoid the problem that essentially coarse fractions of thebulk material form a residue along the side walls 22′, 22″ of thedischarge trough, the trough 20 according to the invention is providedwith a co-lateral feeding device 60 comprising at least a couple oftransverse feed screws 61′, 61″. These feed screws 61′, 61″ aresymmetrically arranged on each side of the belt conveyor 28 and attendto the feeding of bulk material from the region beside the belt conveyorPreferably, the feed screws are made progressive, whereby a supply ofbulk material to the feed screw will be possible essentially along theentire length of the feed screw.

In FIG. 7 a view of a preferred embodiment of the invention is shown inperspective from the front. In this embodiment the trough 20 comprises,besides the above mentioned beam construction 30 with three transversebeams 31, 32, 33, also three pairs of transverse, substantiallyparallel, progressive feed screws 61′/61″, 62′/62″, 63′/63″. Said threepairs of progressive feed screws are symmetrically arranged in the screwtrough on each side of the belt conveyor 28 adjacent to the bottomportions 24′, 24″. In the preferred embodiment the three pairs ofprogressive feed screws have a gradually increasing length l₁, l₂, l₃.The respective feed screw is placed so that its discharge end endsadjacent to the edge of or on top of the conveyor belt 25 in a regionbehind a transverse beam. The respective feed screw is journally mountedin the side wall 22′, 22″, where it also is connected to a drivingdevice 60′, 60″.

The first pair of transverse, progressive feed screws 61′/61″ is placedessentially in alignment with a symmetry line which is common for saidfeed screws 61′ and 61″. Further, they are placed in front of the firsttransverse beam 31, seen in the transport direction of the conveyorbelt, so that the respective discharge end ends in a region in front ofthe first transverse beam 31. The respective feed screw in the firstpair of feed screws 61′/61″ has a length l₁, which substantiallycorresponds to the width of the respective bottom portion 24′, 24″, andits discharge end ends in close connection to the longitudinal side ofthe conveyor belt 25, just outside the edge of the respective bottomportion 24′, 24″.

According to the preferred embodiment of the invention, also a secondpair of transverse, progressive feed screws 62′/62″ are placedsubstantially parallel with the first pair of feed screws 61′/61″ andessentially aligned with a symmetry line which is common for said secondpair of feed screws 62′/62″. They are placed in front of the secondtransverse beam 32, seen in the transport direction of the conveyorbelt, so that the respective discharge end ends in a region in front ofthe second transverse beam 32 and behind the first transverse beam 31.The respective feed screw in the second pair of feed screws 62′/62″ hasa length l₂, which in this case is somewhat longer than the length ofthe first pair of feed screws. Thus, the second pair of feed screws willextend a distance in over the conveyor belt, typically to between abouta third to a half of the width of the conveyor belt.

Further, a third pair of transverse, progressive feed screws 63′/63″ isin a similar way placed in front of said transverse third beam 33, whichpair has a screw length l₃, which in this case is somewhat longer thanthe length of both the first and second pairs of feed screws. Thus, thethird pair of feed screws will extend an additional distance in over theconveyor belt, typically to between about a half to three fourths of thewidth of the conveyor belt.

According to this preferred embodiment one may, as initially mentioned,solve the problem with residues of bulk material being created on thebottom portions 24′ and 24″, respectively, with the initially describedproblems in the completed paving as a consequence. Further, it should beunderstood that coarse fractions, which at the dumping fall along theside walls of the discharge trough, will be continuously fed to theconveyor belt during the paving operation. The coarse fractions fed bythe feed screws will also to a certain extent be distributed over thewidth of the conveyor belt by the respective following transverse beam.In this way, a considerably improved homogeneity of the discharged bulkmaterial during the entire paving operation is obtained.

By adjusting the speed of the driving units 60′, 60″ and hence also thespeed of the feed screws 61′-63″, the output of bulk material fromdifferent portions of the sides of the feed trough may be varied.Further, it is understood that the device according to the inventionaccording to the preferred embodiment makes a very flexible operationpossible, where the homogeneity of the discharged bulk material may beoptimised from the current fractionatings in the discharge trough. Byarranging the feed screws after each transverse beam, essentiallycoarse-fractionated bulk material will be fed into each sub-volume, v₁,v₂, v₃ of the total volume V of discharged bulk material. As the feedscrews extend gradually longer in over the conveyor belt, an uniformhomogeneity is also guaranteed over the entire width of the conveyorbelt, where the feed screws also have a certain mixing effect both as towidth and depth.

Further, an additional advantage is achieved, which is connected to theshift of lorries, where the possibility to vary the output fromdifferent regions of the trough enables a quicker emptying of the lorryplatform so that more time for shift of lorries may be obtained. Byreducing the feeding of bulk material from the region along the sidewalls and instead allow the main portion of the output to be taken fromthe central regions of the hillock, i.e. above the conveyor belt 25, theemptying of the lorry is facilitated, which implies that it will beeasier to make the bulk material to suffice during the entire time ofthe shift of lorry. At the same time, a buffer of bulk material iscreated along the side walls, i.e. in the region on top of the feedscrews. When the lorry has driven away, the discharge from the sides mayfor example be increased so that an essentially homogeneousfractionating is achieved. In this way the problem of spotwise coarsefractions is solved, which fractions appear in connection with the shiftof lorries at conventional paving operations of longer paving distances.

In FIG. 8 a preferred embodiment of the invention is shown in alongitudinal section along the symmetry line VIII-VIII in FIG. 7. As canbe seen from the figure, the feed screws 61′, 62′ and 63′ are placed ina semi-cylindrical discharge channel 70 each arranged in the bottomportion 24′. In front of the respective feed screw the bottom portionhas a surface 24 a′, 24 b′, and 24 c′, respectively, which inclinestowards the feed screw. The bottom portion 24 rises behind the feedscrew as a substantially vertical wall 71. Otherwise, the belt conveyor60, 25, 26, the transverse beams 31, 32, 33 and the rear wall 21 of thetrough are indicated.

The progressive properties of the feed screws 61′-63″ are simplestachieved by permitting the core diameter to have a gradually decreasingdiameter in the feeding direction at the same time as its outer threaddiameter G₁, G₂, G₃, and thread pitch are kept constant. Thus, thestarting end of the feed screw, at said side walls 22′ and 22″, has alarger core diameter D₁, D₂, D₃, and a smaller core diameter d₁, d₂, d₃in the final end of the feed screw. In this way, the advantage isachieved that the feed screws 61′ to 63″, which in their feedingdirection successively reduces their core diameters and correspondinglyincreases their thread heights, give a contribution of bulk materialessentially along the entire length of the feed screw.

It has proved that the above design contributes to an effectivedischarge of bulk material, especially if the feed screws are given adirection of rotation which implies that the upper side will move in thesame direction as the conveyor belt, i.e. from the front and backwards,which is indicated with arrows in the figures. The movement of the bulkmaterial falling down towards the transverse progressive feed screws61′, 62′ and 63′ will be facilitated in a direction towards therespective feed screw by influence of the respective sloping plane 24a′, 24 b′, 24 c′, respectively, in front. Further, the bulk materialwill be driven backwards in the trough, which corresponds to themovement direction of the belt conveyor and also to the movement of thebulk material being dumped from the lorry platform. This implies thatthe relative movement between the bulk material and the feed screwsdecreases, which reduces the wear on the equipment and contributes toreduced energy consumption.

The invention also comprises a beam and a frame comprising at least onebeam which are intended to be used in a conventional trough fordischarge of bulk material. The beam may be afforded a varied shape, ashas been described above. It is transversely placed in a suitable mannerabove the belt conveyor, so that some of the bulk material, which by thebelt conveyor is carried in the direction against the outlet, is sloweddown. It is also conceivable to arrange the beam in a frame which isplaced on top of the belt conveyor. Especially, if several transversebeams are desired, a frame comprising several beams may be used.Suitably, the frame comprises two opposite side plates/beams, in whichat least one transverse beam is arranged in a suitable manner. The framemay easiest be arranged above the belt conveyor by placing it on top ofthe belt conveyor, so that the side plates/beams will rest against theprotection plates which normally cover the driving chains of the beltconveyor. It is also conceivable to arrange the transverse beams at adesired distance from each other and at desired heights along acentrally arranged beam. This centrally arranged beam may for instancebe designed such that it is placed on top of the beam constitutingprotection for the centrally placed driving chains of the belt conveyor.In this way, the beam constructions may be kept in place, especially ifone or more of the transverse beams are designed so that they abut thebottom portions of the trough. Normally, the frame with this embodimentshould not need to be fixed in the trough as it will be kept in place,partly by the weight which the bulk material exerts, partly by the forcewhich is developed when the belt conveyor forces the masses against theoutlet. The frame will then be pressed downwards towards the basis andbackwards towards the rear wall of the trough. Preferably, the framecomprises also a transverse beam in the front edge of the frame, whichbeam may advantageously be designed such that it constitutes the firsttransverse beam above the conveyor belt. The frame is suitably designedin such a way that the discharge conditions characteristic for theinvention may be obtained. In other words, the first transverse beamshould be arranged further from the outlet arranged on the platform thanthe second beam and preferably it should be arranged in the front halfof the trough. Preferably, the front beam is also arranged at a lowerheight above the conveyor belt than the following one/s.

EXPERIMENTS IN LABORATORY SCALE

Experiment 1

In order to investigate the discharge progress from a conventionaltrough 20 with a belt conveyor 28, experiments were performed inlaboratory scale. A model of a trough 50 was manufactured. The modelcomprises a front wall 50′ with an inlet for the belt conveyor 28 in thelower portion with a width covering the entire bottom of the trough, arear wall 50″ with an outlet for the belt conveyor and two side walls ina transparent material, which are not illustrated in the FIGS. 9 a to 9c. In order to imitate a conventional discharge trough the height of theoutlet in the rear wall was made larger than the height of the inlet inthe front wall.

In FIGS. 9 a to 9 c a sequence of an output of bulk material in aconventional trough is schematically shown. The bulk material used inthe experiment constituted of sand which had been stained to elucidatethe flow progress during the discharge. The stained sand was filled intothe trough in essentially uniform horizontal layers 51 to 54, where thelayers are illustrated with different patterns.

In FIG. 9 a the trough is shown before the discharge has started and itis illustrated how substantially uniform layers had been arranged in themodel, from the uppermost layer 51 to the lowermost layer 54. When thedischarge started, the belt conveyor 28 with the conveyor belt 25 and anumber of carriers 26 moved in the direction from the front wall 50′ tothe rear wall 50″, whereby an empty compartment, i.e. the region whichis the result of the distance between two carriers 26, will enter thetrough through the inlet in the front wall 50′.

FIG. 9 b shows how the layer structure looks when the discharge has beenin progress for a while. At the experiment it was established that themajor part of the discharged bulk material is filled in this emptycompartment, substantially by bulk material falling down along the wall50′, which is shown in FIG. 9 b. At the experiment, also a certainfilling was observed in the section leaving the trough 50 and thus alsoa certain fall took place along the inside of the wall 50″.

Through fall bulk material is continuously refilled against the wall50′, and partly against the wall 50″, in the same amount as discharged.On the other hand, it could be established that bulk material whichinitially laid substantially in the middle of the trough, i.e. at adistance behind the front section of bulk material where a continuousfall occurs and also at a distance in front of the section adjacent tothe rear wall of the trough where a certain smaller fall takes place, isnot influenced by the belt conveyor on the whole. From this centralregion no/very little bulk material is discharged and the bulk materialmaintained essentially its original position.

FIG. 9 c shows how the layer structure looks when the discharge has beenin progress for another while. From the experiment it could beestablished that concurrently with bulk material being transported awayfrom the front portions of the trough, substantially adjacent to thefront wall, i.e. in direct connection to the inlet for the beltconveyor, a fall occurs from the surface of the rear portions of thehillock, while bulk material in the middle of the hillock hasessentially kept its layer structure. To an essentially smaller extentan output of bulk material occurs in direct connection to the outlet inthe rear wall 50″ with corresponding smaller fall as a consequence,which can be seen in the figure.

This results in a very characteristic, to a certain extent rotatingmovement of the bulk material in the hillock, which very well coincideswith the experiences available from the discharge in full scale withconventional troughs of the kind described. It is understood that such adischarge progress implies great problems to obtain an uniformhomogeneity of the discharged bulk material, where coarse-fractionedmaterial is substantially placed along the front and rear wall of thetrough and finer fractions lie in the central portions of the hillock.

Experiment 2

In order to examine the discharge from a trough 20, which had beenprovided with a beam construction 30 according to the invention, anexperiment was performed in laboratory scale. The model described abovewas provided with transverse beams 31, 32, 33, which were arranged at agradually increasing height above the belt conveyor 28 in the transportdirection. Like the first experiment, stained sand was filled into thetrough in essentially uniform horizontal layers 51 to 54, which is shownin FIG. 10 a.

FIG. 10 b shows how the layer structure looks when the discharge hasbeen in progress for a while. As can be seen from the figure, adischarge progress is obtained with quite another characteristic thanpreviously. Thanks to the invention a considerably more uniformdischarge of bulk material from the lowermost layer is obtained, whichis understood by the fact the upper surface of the hillock is maintainedcomparatively horizontal and that the different layers sinkcomparatively uniformly during the discharge. This indicates that ineach section of the hillock, i.e. in each region behind and/or betweenthe respective beam 31, 32, 33, a little sub-volume of bulk material istaken out.

In FIG. 10 c it is shown how the layer construction looks when thedischarge is almost finished. As can be seen from the figure, the layerconstruction is maintained during the entire discharge, which impliesthat a uniform output of bulk material from the lower layers of thehillock takes place during the entire discharge. It is understood thatwith such a discharge progress the bulk material discharged from thetrough will contain a contribution from all sections in the trough.Thus, the discharged bulk material will contain a certain amount ofcoarse-fractioned bulk material from the front and rear sections of thehillock and a certain amount of finer fractions from the more centralsections of the hillock. Thus, discharge of a more homogenous bulkmaterial may be offered.

Experiments in Full Scale

The device according to the invention was tested at paving of asphalt onroads and was compared with paving with a reference machine of aconventional type. The device of the invention comprised a conventionaltrough with a belt conveyor, which had been provided with transversebeams and feed screws according to the most preferred embodiment of theinvention as per FIG. 7. The conventional trough was of the kind shownin FIG. 1, i.e. it comprised a belt conveyor but none of the beams andco-lateral feed screws according to the invention. When paving with theconventional trough the coarse-fractioned residue of bulk material whichhad initially accumulated along the side walls of the trough was givento remain during the entire paving operation as has been describedabove.

The result from the experiment shows that the homogeneity of thedischarged asphalt has been essentially improved. The longitudinalstrands of fractionated asphalt which are formed at conventional pavingoperations have also been minimized, which is apparent from the diagramin FIG. 11.

In FIG. 11 a diagram shows the average density of the asphalt along apaving distance for the reference machine and for the device accordingto the invention. The bars of the diagram describe the average valuesfrom a number of measurements made at measurements points along thepaving distance. The measurement points are at the right border, rightwheel track, centre, left wheel track and link border of the road. Ascan be seen from the diagram the density, i.e. the average value of thehomogeneity of the asphalt has increased from 2,272 kg/m³ for thereference machine to 2,317 kg/m³ for the device according to theinvention. Further, it can be seen that the difference in averagedensity between the measurement points has decreased, which alsoindicates an improved homogeneity, which is shown in the table below.

Difference in average density [kg/m³] Reference Improvement Measurementpoint machine Invention [kg/m3] Right border - right 125 67 58 trackRight track - centre 56 37 19 Centre - left track 33 16 17 Left track -left 100 103 −3 border

At the experiment, an obvious improvement of the density of the road wasobtained, which indirectly is a measurement of the homogeneity of thepaving. The deviation at the left boarder is explained by the fact thathere the paving was made against another paved surface, which resultedin the surface compactor riding on the already paved surface and couldthus not compact the asphalt sufficiently. Probably, the left border hadshown the same improvement as the right border, if it had been thequestion of paving against a free edge. The right border shows thegreatest improvement, from a density of 2,210 kg/m³ for the conventionaldevice to 2,300 kg/m³ for the device according to the invention, whichcorresponds to a density increase of 90 kg/m³. The considerably improvedhomogeneity contributes to the entire width of the paving reaching amore uniform and higher quality. Further, this implies that the lifetime of the entire paving is lengthened considerably.

A comparison of the size of the so called risk surface occurring at theshifts of lorries was also made. The risk surface was measured by meansof a thermo-camera, which gives a measure of the density and hence thequality of the paved surface could be evaluated. The risk surfaces arethose surfaces of the paving which are considered to have an impairedquality, which will imply premature wear and need of early repairs. Anaverage value of 12 load shifts with the reference device gave a risksurface of 4.8 m², while the device according to invention gave anaverage value for 9 load shifts of 0.6 m².

Experiments in full scale also showed that it was possible to increasethe paving speed, i.e. the paving machine could drive at a highervelocity and still reach a very good quality of the paved surface, i.e.a paved surface with improved homogeneity and high density as comparedwith the reference machine. At the experiments the paving speed could beincreased by as much as 60% and it should be understood that thiscontributed to an improved production economy.

At repairs of existing worn roads, preferably motorways, sections of theold paving is milled off so that a so called milled box is formed wherenew asphalt is paved. In the joint between the existing paving and thenew paving in the paving direction it has conventionally been difficultto obtain sufficient density and here frost erosion damages often occurbecause of moisture penetrating into the paving. Thanks to theinvention, it has proved that these problems may be reduced and eveneliminated, as the discharged asphalt has a considerably improvedhomogeneity.

ALTERNATIVE EMBODIMENTS

The invention is not limited to the above description but may be variedwithin the scope of the appending claims. Within the scope of theinvention, it should be understood that the number of transverse beamsand the number of feed screws may be varied from at least one beamand/or feed screw and upwards, as well as the location of the beamsand/or feed screws, i.e. the height above the belt conveyor, attachmentangles and relative positions. If the height of the location of thebeams above the belt conveyor is varied, it is possible to control theoutput of bulk material in different sections of the hillock. It is alsoconceivable that one or several of the objects of the invention may bereached by arranging several beams vertically, to place the beams atessentially the same or gradually decreasing height above the conveyorbelt. Further, it may imply an advantage if the beams are notperpendicularly arranged above the conveyor belt but obliquely, possiblyalternately inwards and outwards, whereby an advantageous movement ofthe bulk material in the hillock could be obtained.

It is also conceivable that additional advantages may be reached if thebeams are not arranged quite horizontally and if the beams are given acurved shape so that the height of the respective beam above the beltconveyor varies transversely. It is understood that the cross-section ofthe transverse beams may be varied. For instance, transverse beams withthe shape I, U, L may be used or beams with round or ovalcross-sections. For instance, by giving the beams a non-circularcross-section and having them rotatably mounted, the height of therespective beam above the conveyor belt may be adjusted comparativelysimply.

Further, it is understood that the driving of the feed screws may bevaried. In the simplest way, the feed screws are driven by said drivingunits consisting of a motor and a transmission, e.g. a worm gear, a beltor chain transmission, where the motor and transmission may be connecteddirectly to the respective feed screw. Alternatively, the feed screwsare driven by a motor and a transmission, which coupled together driveseveral feed screws.

Further, the design of the trough may be varied. For instance, thetrough need not necessarily be provided with side walls, if the bottomportion is instead made wide and long enough, so that the bulk materialbeing dumped onto the bottom portion cannot fall over the edge.Especially, this embodiment is suitable if the invention is providedwith co-lateral feed screws. Further, a plurality of belt conveyors maybe arranged side by side, alternatively the width of the conveyor beltsmay be increased so that the bottom portion of the trough principallyconstitutes of only one belt conveyor. In such a case, this embodimentrequires no co-lateral feed screws. Further, the outfeeding device maybe one or several feed screws instead of a belt conveyor. If the feedscrew/screws are progressive the need of the beam/beams above them isminimised or even eliminated.

The invention claimed is:
 1. A device for the treatment of bulk materialcomprising: a platform for supporting bulk material; at least oneoutfeeding device arranged on the platform for feeding of bulk materialplaced on the platform towards an outlet arranged on the platform,wherein the outfeeding device has a feeding direction towards theoutlet; and a first and a second beam which both are arranged on theplatform above the outfeeding device, wherein said first and secondbeams extend transverse to the feeding direction of the outfeedingdevice and over at least a portion of the width of the outfeedingdevice, the second beam, in the feeding direction of the outfeedingdevice, is closer to the outlet than the first beam, wherein the secondbeam is at a higher level above the outfeeding device than the firstbeam, a plurality of feed screws arranged on each side of the outfeedingdevice in the feed direction of the outfeeding device, the plurality offeed screws being arranged to feed bulk material from a region outsidethe outfeeding device towards the outfeeding device and onto theoutfeeding device in a feeding direction of the plurality of feed screwswhich is at least partly directed transverse to the feeding direction ofthe outfeeding device and each of the plurality of feed screws beingplaced behind or in front of one of the beams, so that the dischargeends of the respective feed screws end in a region behind the respectivebeam or in a region in front of the respective beam.
 2. A deviceaccording to claim 1, wherein the device contains more than two beamsarranged above the outfeeding device, and the beams, in the feedingdirection, are at an ascending level above the outfeeding device.
 3. Adevice according to claim 1, wherein at least one of the feed screws hasan open volume between the threads of said at least one of the feedscrews, which volume increases in a direction towards the outfeedingdevice.
 4. A device according to claim 1, wherein at least some of theplurality of feed screws extend in over the outfeeding device, andwherein a first feed screw of the plurality of feed screws which isarranged closer to the outlet extends further in over the outfeedingdevice than a second feed screw from the plurality of feed screws thatis arranged further away from the outlet.